With the rapid development of microelectronic technology and the process technology, the computer and peripheral equipments are getting more and more popular in the enterprises and families, wherein the input and out devices of the peripheral equipments are frequently being used to fit the current multimedia trend. Besides, in the present age of digitization, the scanner is a popular input device used to convert the analog information recorded on a sheet or paper into digital format for conveniently storing in a computer.
Referring to FIG. 1, which is a schematic view showing the structure of a conventional automatic document feeder (ADF). The automatic document feeder 100 comprises a sheet-inlet tray 101, a sheet-outlet tray 102, a pick up roller 103, a separation roller 104, a separation pad 105, a feeding channel 110, a first feeding roller module 106, a second feeding roller module 107, a scanning window 109, and an ejecting roller module 108. The first feeding roller module 106 comprises a first feeding driving roller 1061 and a first feeding idle roller 1062. The second feeding roller module 107 comprises a second feeding driving roller 1071 and a second feeding idle roller 1072. The ejecting roller module 108 comprises an ejecting drive roller 1081 and an ejecting idle roller 1082. The pick up roller 103 is disposed adjacent to the sheet-inlet tray 101, and the separation roller 104 which is adjacent to the pick up roller 103 is disposed above the separation pad 105 and contacted with it. The separation roller 104 and the separation pad 105 are arranged adjacent to the feeding channel 110. In the feeding channel 110 of the automatic document feeder 100, the documents 120 will be transported and relayed by the first feeding roller module 106, the second feeding roller module 107, and the ejecting roller module 108. In addition, a scanning window 109 is disposed between the second feeding roller module 107 and the ejecting roller module 108 for reading the image of the document 120. Besides, the sheet-outlet tray 102 is disposed adjacent to the ejecting roller module 108.
When the automatic document feeder 100 starts to operate, the stack of document 120 on the sheet-inlet tray 101 will be fed by the rotating pick up roller 103 and transported to the nip between the separation roller 104 and the separation pad 105. Because the friction between the separation roller 104 and the uppermost sheet is larger than the friction between the fed sheets or that between the lowest fed sheet and the separation pad 105, the separation pad 105 insures that only the uppermost sheet 120 contacting with the separation roller 104 will be transported into the feeding channel 110. When the sheet 120 passes through the separation roller 104 and the separation pad 105, it will be transported into the feeding channel 110, wherein, the first feeding roller module 106 driven by the first feeding driving roller 1061 is arranged to transport the sheet 120 moving on to the second feeding roller module 107. And the second feeding roller module 107 driven by the second feeding drive roller 1071 is arranged to transport the sheet 120 passing through a scanning window 109 where the image recorded on the sheet 120 could be read by a scanning device (i.e. flat scanner) which is disposed under the scanning windows 109. Finally, the sheet 120 will be ejected by the ejecting roller module 108 which is driven by the ejecting drive roller 1081, and will stay on the sheet-outlet tray 102 which is disposed adjacent to the ejecting roller module 108. In addition, the above-mentioned idle rollers are commonly-used elements and known by the person having ordinary skill in the art and no more details about that will be described in the text.
The dimension of the conventional automatic document feeder 100 is large because a plenty of components, such as the pick up roller 103, the separation roller 104, the separation pad 105, the first feeding roller module 106, the second feeding roller module 107, and the ejecting roller module 108, must be installed within the automatic documents feeder 100. Besides, the sheet transporting process of the conventional automatic document feeder 100 is unstable and the scanning quality is not good because the roller modules 106, 107 and 108 disposed in the conventional automatic document feeder 100 for transporting the document 120 are composed of the driving rollers 1061, 1071, 1081 and the idle rollers 1062, 1072, 1082 and the driving rollers and the idle rollers are interacted via point-to-point contacting. The point-to-point contacting will impact the transport quality of sheet and result in bad image quality. Furthermore, in the conventional automatic document feeder 100, the interaction between the drive roller 1061, 1071, 1081 and the idle roller 1062, 1072, 1082 are driven by gears (not shown), a rotation speed difference between the gears and the rollers 1061, 1062, 1071, 1072, 1081, 1082 will make an unstable sheet transportation and result in a dissatisfied scanning quality of the conventional automatic document feeder 100, or will even make the sheet 120 subjected to a wrinkling or tearing damage.